A system and method are disclosed for use when starting an electric motor used in an industrial drive such as a paper mill, or several electric motors simultaneously.
Automation has increased the number of applications in which machines are started from control rooms or away from the site without visual contact with the machine. Drives in which such situations occur are used in the paper industry and various hoist drives. Safety and protection systems have been implemented to protect personnel, machinery and equipment from injury and damage. The safety aspect is important both financially and in terms of the working environment and working comfort, and mandatory regulations have been issued in several areas.
For example, paper making and finishing machines require a function known as a start-up alarm before any part of the machine is allowed to be started. A simple horn or horns controlled by digital outputs from the control system of paper machine drives have been used for this purpose. With safety requirements further increasing, even stricter criteria for alarm devices have been developed and are under development. For example, the safety standard for paper making and finishing machines EN1034-1 (CEN, European Committee for standardization: EN 1034-1:2000, “Safety of machinery—Safety requirements for the design and construction of paper making and finishing machines”, approved 17 Sep. 1999), currently requires a level of safety corresponding to Category 2 as defined in the standard EN954-1 (CEN: “Safety of machinery—Safety-related part of control systems, approved 11 Jul. 1996). According to Category 2, a fault in an alarm device must be detected.
Prior art solutions for detecting a fault in an alarm device include, for example, the one described in the publication U.S. Pat. No. 5,652,566. An acoustic sensor is fitted beside the alarm device, and the sensor must detect the alarm sound and provide the control unit with a feedback signal. In the absence of a feedback signal, another alarm device is activated. The use of an acoustic sensor in an industrial environment requires an analysis of detected noise in order to reliably determine whether the sound originates from an alarm device or another source. Environmental sources of noise in an industrial facility can vary considerably depending on the location, which makes analysis even more difficult. On the other hand, people with normal hearing can distinguish between relatively quiet sounds despite background noise.